1. Field of the Invention
The present invention relates in general to furnace burners, and in particular to a new and useful spin vane for fossil fuel-fired burners.
2. Description of the Related Art
Among the key physical features of burners used in industrial and utility boilers are the spin vanes which typically are located in at least one annular secondary air flow passage that surrounds the burner fuel nozzle. These spin vanes function to change the flow direction of incoming secondary (combustion) air and to impart a swirl velocity on the air as it exits the burner and mixes with the burning fuel. The imparted swirl velocity changes the air-fuel mixing characteristics of the burner and by so doing affects the emission production level and unburnt carbon losses of the combustion process. The spin vanes usually are fabricated from flat sheet metal, and they may be situated in the annular air flow passage(s) so that they are either stationary or movable in relation to the incoming air. Where the spin vanes are movable, they often may be adjusted from a completely closed position to a fully opened position. Movable spin vanes can be useful in instances where field tuning a burner is needed to meet certain performance requirements specified by a burner user.
Spin vanes may be used in both single and dual register burners. FIG. 1 illustrates a known single register burner 10 of The Babcock and Wilcox Company (BandW) with spin vanes 11 located in annular secondary air flow passage 12 which surrounds burner nozzle 13. Pulverized coal and primary air, which serves principally as a coal transport medium, are supplied to burner 10 at inlet 14. Secondary air is delivered to annular secondary air flow passage 12 from windbox 15 which is positioned concentrically about passage 12. Secondary air flow from windbox 15 to passage 12 can be controlled by sliding air damper 16. Burner nozzle 13 and passage 12 respectively deliver the pulverized coal/primary air mixture and the secondary air to the interior of furnace 17 through opening 18 in furnace wall 19. As indicated in FIG. 1, spin vanes 11 induce a swirled air flow pattern which is directed into a burner flame.
FIG. 2 depicts a known dual register burner 20, also of BandW. Like the single register burner 10, the dual register burner 20 has a burner nozzle 13, a pulverized coal/primary air inlet 14 and a sliding damper 16. Dual register burner 20 is distinguishable from single register burner 10 by inner secondary air zone 22 and outer secondary air zone 24, both of which air zones encircle burner nozzle 13 and thereby serve as passages through which secondary air is delivered to the interior of furnace 17. Secondary air zones 22 and 24 are separated from one another by air separation plate 25 which is positioned concentrically about burner nozzle 13. Inner secondary air zone 22 and outer secondary air zone 24 have movable spin vanes 26. Outer secondary air zone 24 also has stationary spin vanes 28 located upstream of movable vanes 26 situated in the outer air zone. As indicated in FIG. 2, inner and outer secondary air mixing patterns respectively exit from inner secondary air zone 22 and outer secondary air zone 24 and are directed into a burner flame.
For further clarity, FIG. 3 shows an enlarged profile view of the known spin vanes 11 and 26 which have been pointed out respectively in FIG. 1 and FIG. 2, above. As shown in FIG. 3, the plate-like spin vane is defined by base edge 31, leading edge 32 which intersects one end of base edge 31 at obtuse angle A, trailing edge 33 which intersects the other end of base edge 31, also at obtuse angle A, and curved outer edge 34 which intercepts the ends of leading and trailing edges 32 and 33, which are farthest from base edge 31.
U.S. Pat. No. 1,620,180 discloses angled vanes with a projecting flange. The flange, however, is not placed in a flow path and is fixed to the vane for support purposes, and not for air flow direction.
U.S. Pat. No. 2,647,568 discloses vanes or ribs which are inclined relative to the burner""s axis. While the vanes or ribs have flared and contoured surfaces, they do not have any extension perpendicular to part of the length.
U.S. Pat. No. 2,515,813 is a further example of angled vanes without an extension.
U.S. Pat. No. 3,049,055 discusses optimum vane angularity.
The present invention relates to various embodiments of a novel spin vane of the type used in fossil fuel-fired burners. More particularly, in a first embodiment three separate and distinct flat sheet metal elements are assembled and oriented relative to one another so as to provide a multi-piece spin vane which may be called a compound burner vane (CBV) or compound spin vane (CSV). The sheet metal elements are an outer vane element, an inner vane element and a rail element. Both outer and inner vane elements are aligned perpendicularly with respect to outer and inner faces of the rail element and are positioned so that the outer vane is attached to the outer face of the rail and the inner vane is attached to the inner face of the rail. While the outer and inner vane elements may be aligned relative to one another so that they divert the secondary air flow in the same direction both outside and inside of the rail element, the vane elements may be angled in relation to one another, preferably at an angle ranging from ten (10) to forty (40) degrees, so that they will divert the air flow in differing directions. Additionally, the profiles of either or both of the vane elements may be altered to create converging or diverging air flow patterns. A ratio of outer vane element height to inner vane element height (ho/hi) also may be established to provide an air flow pattern that is optimized for specific burner requirements. The structure of the invention has been found to change the secondary air flow characteristics of the known single register burner so 5. as to mimic those of the known dual register burner. Previous measurements suggest that certain combustion-generated pollutants are lower for the dual register burners than for their single register counterparts. Thus, the invention, when applied to a known single register burner that has already been put into service, allows the burner to be quickly and inexpensively modified so that the level of its emissions are reduced to a point which is comparable to that of the known dual register burner and so that the flame produced by the modified single register burner is shorter than that of the known dual register burner. The invention also may be used in the known dual register burner in the event that a need should arise to achieve emission standards more stringent than those currently encountered by users of the known dual register burner.
Accordingly, one aspect of the present invention is drawn to a multi-piece spin vane which may be used in an air passage of either a single register or a dual register fossil fuel-fired burner, and this vane is comprised of:
A plate-like, rectangular-shaped rail element oriented in the air passage such that an outer face of the rail element is directed toward an outer wall of the air passage and an inner face of the rail element is directed toward an inner wall of the air passage;
A plate-like outer vane element which has a base edge, leading and trailing edges and an outer edge, and which is fastened at the base edge to the outer face of the rail element so that the outer vane element and the outer face of rail element are perpendicularly aligned; and
A plate-like inner vane element which also has a base edge, leading and trailing edges and an outer edge, and which is fastened to the inner face of the rail element so that the inner vane element and the inner face of the rail element are perpendicularly aligned.
Another aspect of the present invention is drawn to a fossil-fueled burner apparatus having means for providing a fossil fuel to an outlet end of the burner apparatus for combustion, a single annular air flow passage partially defined between an inner wall and an outer wall of the burner apparatus, and an arrangement of multi-piece spin vanes of the aforementioned construction installed and positioned within the annular air flow passage for imparting a spin to combustion air flowing through the annular air flow passage.
Yet another aspect of the present invention is drawn to a another form of a compound spin vane for imparting a spin to combustion air flowing through an annular air flow passage of a fossil-fueled burner apparatus, the passage being partially defined between an inner wall and an outer wall. This form of the compound spin vane comprises a first vane portion having a leading edge exposed to the oncoming flow of air, and a trailing edge located downstream thereof with respect to the flow of air as it passes by the first vane portion. The first vane portion also has an inner edge, and an outer edge located proximate to the outer wall of the annular air passage. The first vane portion also has opposite, lateral sides. A second vane portion having a leading edge exposed to the oncoming flow of air, a trailing edge downstream thereof with respect to the flow of air as it passes by the second vane portion, is also provided. The second vane portion also has an inner edge located proximate to the inner wall of the annular air passage, an outer edge, and opposite, lateral sides. Finally, means are provided for rigidly connecting a first lateral side of the second vane portion to one side of the first vane portion in spaced lateral relationship with respect to the first vane portion so that both the first and second vane portions move together as a unit when the compound spin vane is installed and positioned in the annular air flow passage of the burner apparatus.
Yet still another aspect of the present invention is drawn to a fossil-fueled burner apparatus having means for providing a fossil fuel to an outlet end of the burner apparatus for combustion, a single annular air flow passage partially defined between an inner wall and an outer wall of the burner apparatus, and an arrangement of compound spin vanes installed and positioned within the annular air flow passage for imparting a spin to combustion air flowing through the annular air flow passage, wherein some of the compound spin vanes comprise the foregoing construction.
Another aspect of the invention is to provide a compound burner vane (CBV) which is simple in design and is more economical to manufacture than single-piece vanes having complex shapes. As suggested from the foregoing summary, the invention also provides a user of existing single register burners with a low cost alternative to replacing such burners with higher cost dual register burners in order to reduce boiler emissions. By replacing existing single register burner vanes with the invention, a burner user also may significantly reduce the amount of boiler down time that otherwise would be required for total burner replacement.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.